Tire Pressure Monitoring Systems (TPMS) play an important role in vehicle safety and emissions reduction. A majority of this market is served by direct tire pressure monitoring systems, in which each tire contains a TPMS sensor module. Thus, a battery powered sensor module is assembled in the inside of a tire to monitor a tire pressure thereof. The sensor module contains a pressure sensor, a microcontroller, a radio-frequency (RF) transmitter, and a coin battery cell.
Principally, the sensor module measures the tire pressure and uses a unidirectional link to transmit the measurement data to a central unit in the vehicle. Since battery cannot be changed, sensor module lifetime is determined by battery lifetime. A major portion of the power consumption is generated by the RF transmission. Hence, it is an important task to reduce power consumption for RF transmission as much as possible.
The sensor module may also have a low-frequency (LF) receiver, which is used to configure the sensor module after mounting sensor module to the tire in the vehicle production or in a repair garage (e.g., in case of replacement modules or firmware update for maintenance of sensor modules which are already in use). Typically, the downlink communication from the sensor module to the vehicle is implemented via the RF transmitter at 315 or 434 MHz, whereas the uplink communication to the sensor module is implemented via the LF receiver at 125 kHz. Thus, two communication devices with two communication channels are used for bidirectional communication between the vehicle and the sensor module.
In order to properly assess each tire, a vehicle must be able to localize each TPMS sensor module, meaning it must be able to know which sensor module is located at which tire position (e.g., front left, rear right, etc.). In former times, manual localization, e.g., programming a fix location into the sensor module, was used. Current technologies allow for automatic localization. However, some vehicles, such as trucks including tractor trailers, have multiple axles, axles without wheel speed sensors, twin tires, and multiple tires in close proximity to each other making it impossible to accurately localize each TPMS sensor module with existing methods. For example, RF Received Signal Strength Indication (RSSI) does not provide the accuracy to distinguish nearby axles or twin tires. In the presence of twin tires, g-sensors (e.g., used in 2 g sensing) cannot distinguish between say the outer left tire and the inner right tire. In addition, Angular Position Sensing (APS) requires the presence of wheel speed sensors, which are typically not present on trailer tires. Additionally, the accuracy of APS may not be sufficient to distinguish nearby axles or twin tires. Thus, current localization techniques may not be sufficient for localizing TPMS sensor modules in such environments. Therefore, an improved TPMS capable of localizing each TPMS sensor module may be desirable.